The invention relates to a valve with a cylindrical valve chamber which surrounds a spring leaf curved in a circular manner in the circumferential direction of the valve chamber and whose circumferential region arranged in the area of an intake directed radially to the chamber wall forms the valve closure, so that under the pressure of the medium to be blocked, the spring leaf can be deflected resiliently into an open valve position. Such a valve is particularly suitable as a delivery valve of a rotary piston compressor, because in the axial direction of the compressor it can be given a random length, whilst being very small in its radial direction. In particular, the valve closure can be positioned very close to the inner wall of the rotary piston compressor, so that this leads to a minimum size of the compressor clearance volume.
For a valve of the above type, a spring leaf has already been proposed which is flat in the untensioned state and only assumes a circular shape after fixing in the cylindrical valve chamber by engaging under pretension with the inner wall thereof. The thus oppositely directed ends of the open circular shape are supported in the hook-like ends of a .OMEGA.-shaped lift guard on the side of the valve chamber diametrically opposite to the intake. As a result with the valve closed the spring lead arranged in a circular manner engages under spring tension on the inner wall of the valve chamber on a relatively large circumferential region of about 130.degree. on the side of the radial intake, whilst the outlet only fills less than a third to a quarter of this angular range. If this spring leaf is deflected under the pressure of the medium flowing through the intake as a result of the engagement of the spring leaf on both sides of the intake in the circumferential direction, corresponding circumferential regions of the spring leaf are supported on the inner wall of the valve chamber, as a result of which the deflection is limited to a reduced circumferential region of the spring leaf with respect to the intake, so that the deflection is linked with correspondingly high bending stresses which, when the valve is used on a compressor lead to fatigue failures in a relatively short time.